KR20050010707A - Screw-tap - Google Patents

Abstract

The present invention relates to a thread-tab with two or more cutting lands with cutting edges. In order to provide thread-tabs with adequate machining reliability even at high cutting speeds, in the present invention, the cutting edges of the cutting lands should be provided with negative angle chamfers, which reduce the inclination angle of the cutting edges, at least at the starting taper. Suggested.

Description

Screw-Tap {SCREW-TAP}

The present invention relates to a screw-tap having two or more cutting lands with cutting edges for cutting female threads.

Various types of thread-tabs for cutting female threads are known in the art.

The configuration of the tab is mainly determined by different kinds of screws that can be formed into the tab. Precision Metric ISO Metric Threads, Tightened Screws, Loosely Threaded, Tapered Screws, Pipe Screws, Whitworth Pipe Screws, Trapezoidal Screws, Buttress Threads, Round Screws, Tapping-Screw Screws, etc. Requires specific thread-tabs for specific applications in order to obtain optimal results. The shape of the tool is also determined by the wear of the hole.

The configuration of the thread-tab is further determined by the requirements for high speed cutting. When using a hand to machine a female thread with a three-part tab, the thread can be cut using a machine with a single tap. To get more throughput with the machine, cutting speeds up to 100 m / min are possible. This necessitates the use of thread-tabs of coated or uncoated cemented carbide.

The possibility of breaking and crushing the tool, and thus the machining reliability achieved with the provided tool, is substantially influenced by chip evacuation out of the hole, especially in the case of high speed cutting. Both the shape of the cutting edge and the shape of the chip grooves penetrating into the workpiece are related to chip evacuation out of the hole. Although ejecting the chip out of the hole is the shape of the chip groove, the shape of the cutting edge determines the cutting and curling of the chip and thus the transfer characteristics of the chip to be discharged out of the hole.

Depending on the material to be perforated, it is known in the art that the inclination angle for the screw-tab ranges from -2 ° to + 20 °. The inclination angle mainly determines the shape of the chip (continuous chip with built-up edge, discontinuous chip or continuous chip) and influences the cutting torque. Again, the shape of the chip determines the discharge characteristics of the chip.

At the required high speed cutting, all known thread-tabs have reached their limits in general requirements for tool life in modern manufacturing processes. Because of improper ejection of chips out of the hole, breakage of the cutting edge or even breakage of the tab often occurs, especially at high speed cutting.

It is an object of the present invention to provide a thread-tab which gives adequate machining reliability, even at high speeds, compared to the prior art.

According to the invention, this object is achieved by providing a thread-tab with two or more cutting edges, the cutting edge having at least a chamfer of the cutting edge at a negative angle which reduces the effective tilt angle of the cutting edge at the starting taper. .

The surface of the chamfer of the cutting edge forms a negative angle with respect to the surface perpendicular to the surface formed by the cutting. This means that the cutting edge is formed by the transition from the flank to the surface of the chamfer, not from the bottom of the chip groove to the flank as in the prior art.

One advantage of the screw-tab according to the invention is that since the chamfer is in a negative shape, the chips formed by the cutting edges are cut more tightly or cut faster than when using a shape with an overall positive tilt angle. will be. As a result, the chip forms a unit that is more compact, often smaller, and can be more easily discharged out of the hole.

The overall shape of the thread-tab may be positive or negative. That is, the inclination angle formed by the cutting surface and the surface perpendicular to the surface formed by the cutting may have a negative or positive value. With the exception of the chamfer with a negative angle, the shape of the tab immediately adjacent to the chamfer remains positive or negative, so that the chip can be removed in a manner suitable for the workpiece. Here, "positive" and "negative" should be understood according to the general provisions for the shape or angle of inclination of the cutting edge.

When constructing the shape of the screw-tab according to the invention, it is advantageous that the angle of the chamfer is -10 ° to -60 °, preferably -30 ° to -45 °, more preferably about -35 °. This angle is measured between the surface chamfered and the surface perpendicular to the surface formed by the cutting. For the most important materials, the shape of the chip that is optimal for chip evacuation is obtained from the above angles.

Embodiments of the invention are preferred in which the width of the chamfer measured in the radial pitch direction is 0.05 times to 0.75 times, preferably 0.1 or 0.2 times to 0.5 times the depth of the profile. The depth of the profile represents the radial distance from the diameter of the screw core to the outer diameter of the tab. Due to the limitation of the width of this chamfer or the area of the cutting surface that is negatively angled relative to the surface perpendicular to the formed surface, the overall chip-deflection shape of the tab remains positive or negative.

In a preferred embodiment of the invention, the chamfer further extends from the guide region to the cutting edge. Then, when the cutting edge located in the guide region of the tab acts, cutting and curling of the chip occur quickly. Thus, the discharge characteristics of the chips cut by the guides of the tabs are also improved.

Also advantageous is an embodiment of the invention in which the width of the chamfer increases from the tip of the screw-tab toward the shank.

In a particularly preferred embodiment, the screw-tab is made of cemented carbide.

Other advantages, features, and possible applications of the present invention will become apparent from the following description and the accompanying drawings, which are described by way of example of the preferred embodiments.

1 is a bottom sectional view of a starting taper of a screw-tab in accordance with the present invention

FIG. 2 is an enlarged view of the cross-sectional area of the tab shown in FIG.

3 is a side view of the screw-tab, and

4 is a three-dimensional cross-sectional view of the starting taper area of the tab.

* Description of reference numerals for major parts of the drawings

1: thread-tap 2: starting taper

3: cutting land 4: cutting edge

5: chip groove 8: flank

9: chamfer 10: cutting surface

12: shank 13: cutting part

14: guide part 15: head

1 is a cross-sectional view of the screw-tab 1 according to the present invention cut out in the region of the starting taper 2. Four cutting lands 3 are shown, each with cutting edges located in the left region radially outward. A chip groove 5 for discharging chips is formed between the lands 3. Depending on the type of hole, the chip groove 5 can be configured as a straight groove (for through bore), or can be configured to be twisted in the forward direction (for blind holes) as in the illustrated embodiment. In the illustrated embodiment the forward twist of the chip groove 5 is shown more clearly in FIG. 3. It is also possible to have a torsional chip groove or a twist in the opposite direction.

As shown in FIG. 1, the cutting land is ground in the radially outer region. Each channel of the thread-tab cuts the workpiece to a certain depth, ie depth of cut. The cutting depth generally corresponds to the profile depth of the tab.

The cutting edge area which internally limits the radial height of the thread and corresponds to the thread inner diameter is indicated by a circle A on one cutting land 3, for example as shown in FIG. 1. Circle A in FIG. 1 is shown enlarged in FIG. 2. The area of the cutting edge 4 of the cutting land 3 is clearly shown. In the radially outer region of the cutting edge there is a ground face. Metal cutting is mainly carried out when the tab is dug into the workpiece with the cutting edge 7. The cutting edge is formed at the point where the cutting surface 10 and the flank 8 meet. An important point in the successful operation of the thread-tab is that in the case of a thread-tab the curved flank 8 has a larger radius in the area of the cutting edge 7 than on the land side away from the cutting edge 7. To have. The curvature of this flank is called a relief. In this way, the tangential angle formed between the surface formed by the cutting and the flank 8, that is, the clearance angle, is increased, thereby preventing the tool from being caught in the workpiece. The chamfer 9 according to the present invention on the cutting surface 10 in the region of the cutting edge 7 is configured to form a negative angle with respect to the surface of which the surface of the chamfer 9 is perpendicular to the surface formed by cutting. have. In the illustrated embodiment, the angle between the surface of the chamfer 9 and the surface perpendicular to the surface formed by the cutting is about -40 °. However, the overall shape of the cutting edge 4 is still defined by the positive inclination angle formed by the cutting surface 10 and the flank 8. The negative angle chamfer 9 only effectively reduces the inclination angle when the cutting depth is relatively small. At the point where the cutting surface 10 and the chamfer 9 meet, another blade 11 is formed as shown in FIG. On this day 11 the chips are ejected and very tightly dried and / or cut.

3 shows a side view of the entire screw-tab 1. The screw-tab 1 is divided into a shank 12 that holds the tab to the chuck and a cutting portion 13 that engages with the workpiece. The cutting portion 13 of the thread-tab 1 can be divided into a so-called starting taper 2 and a guide portion 14. The starting taper 2, the cross section of which is shown in FIGS. 1 and 2, is tapered towards the head 15 of the tab 1. The taper and the increase in the radial pitch as the depth of the tab penetrates into the workpiece increases the amount of material to be removed by each cutting edge 7. The circumference of the tab 1 is largest at the transition between the starting tape 2 and the guide 14. Guide portion 14 is also tapered but is narrower toward the shank. This prevents the guide portion 14 from being caught in the workpiece and prevents damage to the thread or decreases the quality of its surface.

In figure 4 a three-dimensional cross-sectional view of a screw-tab 1 according to the invention is shown. It can be clearly seen that the tapered shape of the starting taper 2 of the tab 1, in which the profile depth of the cutting land 3 increases with increasing depth. In the embodiment shown, the width of the chamfer 9 also increases with increasing depth. The overall cutting shape is positive so that the wedge angle between the extension of the flank 8 and the extension of the cutting surface 10 is less than 90 °, while the chamfered surface is clearly above 90 ° with the flank. To achieve.

According to the present invention, even at high cutting speeds, the thread-tab has a suitable machining reliability, and due to the negative shape of the chamfer, the chips formed by the cutting edges are curled up more or more tightly than when using a shape with an overall positive inclination angle. Cut faster, the chips form units that are more compact, often smaller, and can be more easily ejected out of the hole.

In addition, the chamfer further extends from the guide region to the cutting edge, so that the cutting and curling of the chip occurs quickly when the cutting edge located in the guide region of the tab acts, thus discharging the chip cut by the guide of the tab. The property is also improved.

Claims (8)

In the thread-tab 1 with two or more cutting lands with cutting edges, The cutting edge of the cutting land is characterized in that it has a negative angle chamfer which reduces the inclination angle of the cutting edge, at least at the starting taper. 2. Thread-tab (1) according to claim 1, characterized in that the overall cutting shape of the thread-tab (1) excluding the chamfer is positive. 2. Thread-tab (1) according to claim 1, characterized in that the overall cutting shape of the thread-tab (1) excluding the chamfer is negative. 2. The screw according to claim 1, wherein the angle formed by the cutting surface and the chamfer is -10 ° to -60 °, preferably -30 ° to -45 °, more preferably about -35 °. Tab (1). The screw-tab (1) according to claim 1 or 2, characterized in that the width of the chamfer is 0.05 times-0.75 times, preferably 0.25 times-0.5 times the depth of the profile. 4. Thread-tab (1) according to any one of the preceding claims, characterized in that the chamfer further extends at least part of the cutting edge in the guide region. 5. Thread-tab (1) according to any one of the preceding claims, characterized in that the chamfer width of the starting taper region increases from the tip of the thread-tab toward the shank. Screw-tab (1) according to any of the preceding claims, characterized in that the thread-tab is made of cemented carbide.